KIKAIDER 01: THE ANIMATION

Ever since the fall of the DARK organization, Jiro has been wandering everywhere and wondering if he would ever see Mitsuko again or not. During his journey Jiro meets a beautiful girl named Rieko who is protecting Akira, a little boy from the evil Professor Gill. Ironicly, he's the son of Professor Gill, but he is also the key to Gill’s menacing secret weapon and his plans to conquer the world. (Source: Anime News Network) — Description from AniList community (anilist.co).